Boron Acceptors Research Articles

Impact of the dangling bond defects and grain boundaries on trapping recombination process in polycrystalline 3C SiC

The bulk polycrystalline (pc) 3C SiC of n- and p-type obtained by thermal decomposition of methyltrichlorosilane vapor have been studied by applying the electron paramagnetic resonance (EPR), direct current (DC) conductivity, photoconductivity (PC) and PC time-resolved decay methods. The energy level of the two donor-like minority carrier traps at ε1 = 77 meV and ε2 = 92.6 meV located at the grain boundaries (GB) of pc-3C SiC has been obtained using the measurements of the temperature dependence of DC conductivity and PC in the range of 80–600 K. The minority carrier traps assigned to carbon and silicon dangling bonds with the carbon back bonds were observed in the EPR spectra of pc-3C SiC of n- and p-type at g = 2.0029(3), g = 20042(3), respectively. The PC time decay after the termination of the photo-excitation was studied in monocrystalline and pc-3C SiC of n- and p-type at 80 K. The persistent relaxation of PC has been described by kinetic equations accounting the trapping, ionization, and recombination processes of non-equilibrium charge carriers bound dynamically to shallow donors and acceptors. We have concluded that the main process responsible for the long-lived relaxation of the PC is trap-assisted electron-hole recombination in n-type pc-3C SiC and ionization of boron acceptors, as well as the hole escape/capture at the boron level in p-type pc-3C SiC. The differences in the relaxation process of the PC in n- and p-type pc-3C SiC were explained by the presence of the potential barrier height of about 8.6 meV at GB for the capture of the majority carriers in p-type pc-3C SiC.

Highly efficient blue thermally activated delayed fluorescence organic light emitting diodes based on tercarbazole donor and boron acceptor dyads

Two new blue TADF emitters, 3CzTB and M3CzB, for application in highly efficient organic light-emitting diodes are reported.

On the Two-Phonon Relaxation of Excited States of Boron Acceptors in Diamond

The relaxation of holes from excited states of boron acceptors in diamond with the emission of two optical phonons is studied theoretically. To describe the wave function of acceptor states, an electron-like Hamiltonian with an isotropic effective mass is used. The wave function of the ground state is determined by the quantum-defect method. The probability of the transition is calculated in the adiabatic approximation. It is assumed that the phonon dispersion law is isotropic and the phonon frequency is quadratically dependent on the wave-vector modulus, with the maximum and minimum frequencies ωmax and ωmin at the center and boundary of the Brillouin zone, respectively. A high sensitivity of the probability of the transition to the characteristic of phonon dispersion ωmax – ωmin is revealed, especially for the transition with the energy ET in the range 2ℏωmin ≤ ET 1012 s–1) in the “resonance” range ℏωmin + ℏωmax ≤ ET ≤ 2ℏωmax.

Hole spin echo envelope modulations

Hole spins in semiconductor quantum dots or bound to acceptor impurities show promise as potential qubits, partly because of their weak and anisotropic hyperfine couplings to proximal nuclear spins. Since the hyperfine coupling is weak, it can be difficult to measure. However, an anisotropic hyperfine coupling can give rise to a substantial spin-echo envelope modulation that can be Fourier-analyzed to accurately reveal the hyperfine tensor. Here, we give a general theoretical analysis for hole-spin-echo envelope modulation (HSEEM), and apply this analysis to the specific case of a boron-acceptor hole spin in silicon. For boron acceptor spins in unstrained silicon, both the hyperfine and Zeeman Hamiltonians are approximately isotropic leading to negligible envelope modulations. In contrast, in strained silicon, where light-hole spin qubits can be energetically isolated, we find the hyperfine Hamiltonian and $g$-tensor are sufficiently anisotropic to give spin-echo-envelope modulations. We show that there is an optimal magnetic-field orientation that maximizes the visibility of envelope modulations in this case. Based on microscopic estimates of the hyperfine coupling, we find that the maximum modulation depth can be substantial, reaching $\sim 10\%$, at a moderate laboratory magnetic field, $B\lesssim 200\,\mathrm{mT}$.

Shallow donor complexes formed by pairing of double-donor magnesium with group-III acceptors in silicon

Magnesium in silicon primarily occupies an interstitial site, where it acts as a moderately deep double donor. It has recently been shown that interstitial magnesium can pair with the substitutional acceptor boron to form a shallow single-donor center. In this work, we demonstrate analogous complexing with the other group-III acceptors Ga, In, and Al. We observe the odd-parity excited states of each shallow donor complex in absorption spectra, from which the ionization energies are obtained. These complexes can localize excitons, and we observe the donor bound exciton transitions of all four centers in photoluminescence spectra. The Mg-acceptor complexes are found to obey Haynes rule, which predicts a linear relationship between donor ionization energy and donor bound exciton localization energy.

26‐3: Highly Efficient Boron Acceptor Based Blue Thermally Activated Delayed Fluorescent Emitter

We report two TADF dopants, KHU‐TD01 and KHU‐TD02, combined boron acceptor with our two donor moieties. Fabricated KHU‐TD01 and KHU‐TD02 devices show very high EQE of 37.4 % with CIE (0.16, 0.34) and 12.5% EQE with very good deep blue color coordinates of (0.15, 0.08).

Highly efficient blue thermally activated delayed fluorescence emitters based on symmetrical and rigid oxygen-bridged boron acceptors

Materials that exhibit thermally activated delayed fluorescence are promising for the realization of efficient organic light-emitting diodes. However, finding suitable deep-blue thermally activated delayed fluorescence materials is still challenging. Here, we report two highly efficient deep-blue thermally activated delayed fluorescence emitters, TDBA–Ac and TDBA–DI, containing oxygen-bridged, symmetric and rigid boron acceptor moieties. Both emitters have been designed to have high photoluminescence quantum yield and narrow-band blue emission. TDBA–Ac and TDBA–DI exhibited deep-blue emission and a small singlet–triplet energy gap of 0.06 eV and 0.11 eV, respectively, in toluene. The 20wt%-doped films of TDBA–Ac and TDBA–DI in DBFPO host exhibited high photoluminescence quantum yields of 93% and 99%, respectively. The fabricated TDBA–DI device showed an extremely high external quantum efficiency of 38.15 ± 0.42% in the blue region with low roll-off characteristics of 25.2% at high luminance of up to 5,000 cd m–2. The TDBA–Ac-doped device exhibited a high external quantum efficiency of 21.50 ± 0.22% with deep-blue colour coordinates of (0.15, 0.06). The discovery of two deep-blue organic emitters of light could aid the development of next-generation organic light-emitting devices.

Highly Twisted Donor-Acceptor Boron Emitter and High Triplet Host Material for Highly Efficient Blue Thermally Activated Delayed Fluorescent Device.

New highly efficient thermally activated delayed fluorescence (TADF) dopant materials (PXB-DI and PXB-mIC) for blue organic light-emitting diodes are reported. These materials were designed by combining highly conjugated rigid ring donor moieties and a boron acceptor with a highly twisted configuration to have high TADF performance and minimized self-quenching properties. In addition, a new high triplet energy and hole transport-type host material, 5-(5-(2,4,6-triiso-propylphenyl)pyridin-2-yl)-5 H-benzo[ d]benzo[4,5]imidazo[1,2- a]imidazole (PPBI), is also reported. This host represents deeper blue color owing to keeping the original spectra of emitters. A fabricated blue TADF device with PXB-mIC in the PPBI host exhibited maximum external quantum efficiency (EQE) of 12.5% with a CIE of (0.15, 0.08), which is close to that of the National Television System Committee blue color. The blue TADF device performances of the PPBI host was compared with the electron transport-type 2,8-bis(diphenylphosphine oxide)dibenzofuran (DBFPO) host. The blue TADF device with PXB-DI in the DBFPO host exhibited a maximum EQE of 37.4% in the sky blue region. This study demonstrates that our molecular design concept of new emitters and host is beneficial for future high-efficiency deep-blue TADF devices.

Surface and interface properties of ZrO2/GaAs, SiO2/GaAs and GaP/GaAs hetero structures investigated by surface photovoltage spectroscopy

The surface and interface properties of III–V semiconductor heterostructures are of extreme importance for increasing the efficiency of multijunction solar cells. However, presence of surface and interface states, deteriorate the performance of the devices made from these structures. Therefore, in this work, surface and bulk states of n+ -GaAs substrate, grown by vertical gradient freeze (VGF) method, and GaP/GaAs grown using metal organic vapour phase epitaxy are identified from the surface photovoltage amplitude and phase spectra. The surface states are due to complexes formed by silicon and arsenic while the bulk sates are mainly due to boron acceptor states that are commonly observed in VGF grown n+ -GaAs substrate due to encapsulation of molten flux by B2O5 during growth. The surface passivation effects, by high (ZrO2) and low (SiO2) k dielectrics, on the optical properties of n+ -GaAs remains similar in nature as confirmed from the SPV amplitude and phase spectra. Further, the pre-cleaning of the substrate by chemical treatment followed by dielectric deposition show improved surface passivation as confirmed from SPV and X-ray reflectivity. Interestingly, similar surface passivation results are also observed in GaP/GaAs heterostructures. After identification of surface states and their isolation, carrier redistribution processes occurring at surface, interface and substrate are distinguished using wavelength dependent SPV magnitude and phase spectra of GaP/GaAs. Subsequently, corresponding band alignment diagram along with band bending at the interface for this hetero structure is constructed. Identification of surface and interface states of semiconductor heterostructures by SPV, surface passivation with suitable materials and construction of the band diagram would be useful for increasing the efficiency of advanced multi junction photovoltaic devices.

Двухфононная релаксация возбужденных состояний акцепторов бора в алмазе

The relaxation of holes in the excited states of boron acceptors in diamond is theoretically investigated when two optical phonons are emitted. An electron-like Hamiltonian with an isotropic effective mass was used to describe the wave function of the acceptor states. The wave function of the ground state was found by the quantum defect method. The transition probability was calculated in adiabatic approximation. The dispersion law of phonons was considered isotropic, and the frequency of phonons is quadratically dependent on the wave vector module, with the maximum value, omegamax, achieved in the center of the Brillouin zone, and the minimum, omegamin, at the edge of the Brillouin zone. The high sensitivity of the rates to the characteristic of phonon dispersion, omegamax-omegamin, especially for the transition energy, ET, in the 2homegamin≤ ET<homegamin +homegamax interval was revealed. Depending on the transition energy and dispersion of phonons, the rate of two-phonon relaxation in the low-temperature limit varies from ultra-low values (less than 108 s-1) near the threshold, ET=2homegamin, to ultra-high values (more than 1012 s-1) in the "resonance" region homegamin+homegamax≤ ET≤2homegamax.

Multiphonon Intracenter Relaxation of Boron Acceptor States in Diamond

The relaxation rates are calculated in the adiabatic approximation, in which the steady-state impurity states are taken to be electronic-vibrational (vibronic) states. The probabilities of transitions between these states with the emission (or absorption) of one or several phonons are calculated in first-order perturbation theory on the assumption that the transitions are a result of the violation of adiabaticity. The electron part of the wave function of the vibronic state is described by a simple Hamiltonian with an isotropic effective mass. The wave function of the ground state is determined by the quantum defect method. According to the calculations, a hole relaxes from the excited boron acceptor state, whose energy is 304 meV higher than the energy of the ground state, to the ground state with the emission of two optical phonons with a rate of ~1011 s–1. This value is an estimate from above, since the model of nondispersive optical phonons used in the study overestimates the number of phonon modes, whose participation in relaxation is allowed by the energy conservation law. However, despite the rough approximation, it can be concluded that the multiphonon relaxation of boron acceptor states in diamond is a fast process.

A theoretical study of substitutional boron–nitrogen clusters in diamond

Substitutional clusters of multiple light element dopants are a promising route to the elusive shallow donor in diamond. To understand the behaviour of co-dopants, this report presents an extensive first principles study of possible clusters of boron and nitrogen. We use periodic hybrid density functional calculations to predict the geometry, stability and electronic excitation energies of a range of clusters containing up to five N and/or B atoms. Excitation energies from hybrid calculations are compared to those from the empirical marker method, and are in good agreement.When a boron-rich or nitrogen-rich cluster consists of three to five atoms, the minority dopant element—a nitrogen or boron atom respectively—can be in either a central or peripheral position. We find B-rich clusters are most stable when N sits centrally, whereas N-rich clusters are most stable with B in a peripheral position. In the former case, excitation energies mimic those of the single boron acceptor, while the latter produce deep levels in the band-gap. Implications for probable clusters that would arise in high-pressure high-temperature co-doped diamond and their properties are discussed.

Ultra-High Sensitivity Surface Photovoltage Measurement of Heavy Metal Contamination in Silicon Wafers with Fast Metal Identification

The Surface Photovoltage (SPV) minority carrier diffusion length method is the most sensitive and widely used technique for monitoring heavy metal contamination in silicon wafers starting from crystal growth through various IC processing steps. Relentless IC fabline purity refinement, exhibited by a Fe contamination decrease of about 10 times per decade has been matched by corresponding progress in SPV detection capabilities. An iron contamination limit of mid 107 atoms/cm3 is projected for new IC fablines by the year 2020. For SPV this represents a detection goal for a new generation of metrology. In this paper we discuss this newest version of the SPV technique. The key element is the improvement of accuracy and repeatability of the minority carrier diffusion length determination, demonstrated by the coefficient of variance of 0.01% that is an order of magnitude better than the capability of the previous digital SPV version. This translates directly to an order of magnitude better sensitivity in SPV metal concentration measurements quantified by the change in diffusion length (L) caused by activation of the metal recombination activity. Results are presented for some of the purest state-of-the-art 300mm wafers. They illustrate an ultra-high sensitivity procedure for whole wafer mapping of Fe that includes for the first time a quick Fe identification test. This test is done with very short transient diffusion length measurements made possible by the enhanced precision of the L measurements. The test takes minutes compared to hours or days used in previous SPV measurements. Previous digital SPV metrology incorporated concentration measurements of Fe and Cu. SPV versions for photovoltaics include measurement of light-induced degradation related to boron-oxygen defects. The next generation digital SPV extends this measurement to include other interstitial metals Co, Mn and Cr that at room temperature form stable pairs with substitutional boron acceptors. Identification of the metals and separation of their individual contribution is based on metal-specific features of dissociation and association kinetics of the pairing reaction, Mi+Bs ↔ (Mi Bs), involving interstitial metal donors Mi and substitutional boron acceptors, Bs. Cu is differentiated from the other metals due to different irreversible reactions that change the minority carrier diffusion length. A distinctive feature of the SPV metrology is the use of photo-dissociation of pairs, effective for Fe and Co, but not for Mn and Cr. For the latter two metals, thermal dissociation is used. Thermal dissociation is effective for all pairs, therefore in multi-metal measurement cycles it is used as a post photo-dissociation step. Accordingly, the diffusion length measurement in the initial state, Linit, then after photo-dissociation, LPD, and then after thermal-dissociation, LTD, is used in the example illustrating the case of the simultaneous presence of Fe and Mn. After dissociation, a transient diffusion length measurement is performed which determines the association (pairing) time constant, τp. The value of τp is inversely proportional to metal diffusivity and it increases in the order Co→Fe→Mn→Cr. The digital SPV tool incorporates variable temperature wafer stages facilitating optimization of thermal treatment used in monitoring of dissociation or association kinetics. It is believed that these refinements ensure the latest generation of digital SPV tools will meet the demands of Fe contamination monitoring in IC fablines well beyond the 2020 projection while also enabling for the first time fast heavy metal identification testing.

Short lifetime components in the relaxation of boron acceptors in silicon

We present time-resolved measurements of the relaxation between the orbital states of the shallow acceptor boron in silicon. The silicon host was enriched $^{28}\mathrm{Si}$, which exhibits lifetime broadened absorption lines. We observed a wide range of ${T}_{1}$ lifetimes from 6 ps to 130 ps depending on the excited state and the pump intensity. The fastest transients have not been observed previously in the time domain, and they are caused by the phonon relaxation responsible for the small-signal frequency domain linewidth. We identify the slower components with an ionization/recombination/cascade pathway.

Cryogenic scintillation properties of n-type GaAs for the direct detection of MeV/c2 dark matter

This paper is the first report of n-type GaAs as a cryogenic scintillation radiation detector for the detection of electron recoils from interacting dark matter (DM) particles in the poorly explored MeV/c2 mass range. Seven GaAs samples from two commercial suppliers and with different silicon and boron concentrations were studied for their low temperature optical and scintillation properties. All samples are n-type even at low temperatures and exhibit emission between silicon donors and boron acceptors that peaks at 1.33 eV (930 nm). The lowest excitation band peaks at 1.44 eV (860 nm), and the overlap between the emission and excitation bands is small. The X-ray excited luminosities range from 7 to 43 photons/keV. Thermally stimulated luminescence measurements show that n-type GaAs does not accumulate metastable radiative states that could cause afterglow. Further development and use with cryogenic photodetectors promises a remarkable combination of large target size, ultra-low backgrounds, and a sensitivity to electron recoils of a few eV that would be produced by DM particles as light as a few MeV/c2.

18F-AlF Labeled Peptide and Protein Conjugates as Positron Emission Tomography Imaging Pharmaceuticals

The clinical applications of positron emission tomography (PET) imaging pharmaceuticals have increased tremendously over the past several years since the approval of 18fluorine-fluorodeoxyglucose (18F-FDG) by the Food and Drug Administration (FDA). Numerous 18F-labeled target-specific potential imaging pharmaceuticals, based on small and large molecules, have been evaluated in preclinical and clinical settings. 18F-labeling of organic moieties involves the introduction of the radioisotope by C-18F bond formation via a nucleophilic or an electrophilic substitution reaction. However, biomolecules, such as peptides, proteins, and oligonucleotides, cannot be radiolabeled via a C-18F bond formation as these reactions involve harsh conditions, including organic solvents, high temperature, and nonphysiological conditions. Several approaches, including 18F-labeled prosthetic groups, silicon, boron, and aluminum fluoride acceptor chemistry, and click chemistry have been developed, in the past, for 18F labeling of biomolecules. Linear and macrocyclic polyaminocarboxylates and their analogs and derivatives form thermodynamically stable and kinetically inert aluminum chelates. Hence, macrocyclic polyaminocarboxylates have been used for conjugation with biomolecules, such as folate, peptides, affibodies, and protein fragments, followed by 18F-AlF chelation, and evaluation of their targeting abilities in preclinical and clinical environments. The goal of this report is to provide an overview of the 18F radiochemistry and 18F-labeling methodologies for small molecules and target-specific biomolecules, a comprehensive review of coordination chemistry of Al3+, 18F-AlF labeling of peptide and protein conjugates, and evaluation of 18F-labeled biomolecule conjugates as potential imaging pharmaceuticals.

Многофононная внутрицентровая релаксация состояний акцепторов бора в алмазе

AbstractThe relaxation rates are calculated in the adiabatic approximation, in which the steady-state impurity states are taken to be electronic-vibrational (vibronic) states. The probabilities of transitions between these states with the emission (or absorption) of one or several phonons are calculated in first-order perturbation theory on the assumption that the transitions are a result of the violation of adiabaticity. The electron part of the wave function of the vibronic state is described by a simple Hamiltonian with an isotropic effective mass. The wave function of the ground state is determined by the quantum defect method. According to the calculations, a hole relaxes from the excited boron acceptor state, whose energy is 304 meV higher than the energy of the ground state, to the ground state with the emission of two optical phonons with a rate of ~10^11 s^–1. This value is an estimate from above, since the model of nondispersive optical phonons used in the study overestimates the number of phonon modes, whose participation in relaxation is allowed by the energy conservation law. However, despite the rough approximation, it can be concluded that the multiphonon relaxation of boron acceptor states in diamond is a fast process.

Theoretical Evaluation of the Efficiency of Novel Frustrated Lewis Pairs in the cis-Hydrogenation Reaction of Dimethylacetylene

Frustrated Lewis pairs (FLPs) are the combination of Lewis acid and base motifs where steric hindrance prevents strong adduct formation. Accordingly, the ability of FLPs in small molecule activation and their capability in hydrogen cleavage led to their use in the hydrogenation of a wide range of unsaturated substrates. Here, we investigated theoretically the ability of three intramolecular phosphorus/boron FLPs as bifunctional catalysts in the metal-free hydrogenation of dimethylacetylene to cis-alkene. The mechanism of this hydrogenation reaction, based on the boron acceptor [including –OR substituents (B(OR)2), where R is an aliphatic or aromatic branch] and phosphorus donor, has been explored. Based on the results obtained, it was confirmed that the H2 splitting reaction and the formation of the phosphonium–borohydride motifs for these FLPs are endothermic. It has been shown that these FLPs have a moderate ability in H–H bond splitting. Also, the capability of the boron atom in FLPs on the hydrogenation reaction was investigated. The reduction steps of the mechanism showed an exothermic nature. This result revealed that the presence of the boron as a Lewis acid, with a very limited Lewis acidity, improves the catalytic hydrogenation reaction significantly. Finally, it was confirmed that the proposed FLPs in the cis-hydrogenation of alkynes will be effective.

Luminescence Spectroscopy of Bound Excitons in Diamond (Phys. Status Solidi A 11∕2017)

Since the research on diamond doping remains an issue for electronic applications, the luminescence spectroscopy of bound excitons appears essential to evaluate the properties of shallow dopants in diamond. In this paper (article No. 201700402), the formation and recombination processes of bound excitons in diamond are reviewed for boron acceptors, phosphorus, and arsenic donors. Pulsed and continuous excitations are considered, the latter being currently used for the measurement of donor and acceptor concentrations in diamond.

Luminescence Spectroscopy of Bound Excitons in Diamond

Since the research on diamond doping remains an issue for electronic applications, the luminescence spectroscopy of bound excitons appears essential to evaluate the properties of shallow dopants in diamond. In this paper, the formation and recombination processes of bound excitons in diamond are reviewed for boron acceptors, phosphorus, and arsenic donors. Pulsed and continuous excitations are considered, the latter being currently used for the measurement of donor and acceptor concentrations in diamond.